The present disclosure generally relates to semiconductor devices, and particularly to semiconductor structures including a field effect transistor with a composite high-k gate dielectric stack, and methods of manufacturing the same.
High gate leakage current of silicon oxide and nitrided silicon dioxide as well as depletion effect of polysilicon gate electrodes limits the performance of conventional semiconductor oxide based gate electrodes. High performance devices for an equivalent oxide thickness (EOT) less than 2 nm require high dielectric constant (high-k) gate dielectrics and metal gate electrodes to limit the gate leakage current and provide high on-currents. Materials for high-k gate dielectrics include ZrO2, HfO2, other dielectric metal oxides, alloys thereof, and their silicate alloys.
The EOT of a high-k gate dielectric as measured by the inversion thickness needs to be reduced to enhance the performance of a field effect transistor. However, reduction of the EOT as measured by the inversion thickness is limited by the EOT as measured by the gate leakage current. Thus, while reduction of the EOT as measured by the inversion thickness is desirable, reduction of the EOT as measured by the gate leakage current (which means an increase in the gate leakage current) is not desirable.